Take more than 0.1 mm of tooth away before pulling the handpiece out to check the prep 🙂
Seriously that was how I was like my first few times. I guess I've improved in skill since my first operative patient, though I know the same principles now as I did back then. The biggest difference is my confidence level. I know what I'm looking for and I (usually) know when the prep is ready to be restored. I just do my thing and make a prep quickly yet still carefully. I'm sure given 5, 10 more years I'll cut the time it takes to do that in half and then some.
I was so nervous with the injection but once I held the handpiece and went to work I got so calm. I thought that was the strangest thing but looking back I guess it wasn't since we were pretty well prepared.
Just remember that you'll hardly ever do an 'ideal prep'. Use the principles of cavity design you learned in 1st year while removing all the decay. You know what you're doing.